1. Technical Field
This application relates generally to a system and method for performing auto-location of a wheel in a vehicle and more particularly to a tire pressure monitoring system and method for performing auto-location of a tire pressure monitoring sensor arranged with a vehicle wheel using confidence interval analysis. This application further relates to a tire pressure monitoring system and method for performing auto-location of a tire pressure monitoring sensor using confidence interval analysis which takes into consideration rollback events of wheels.
2. Related Art
In tire pressure monitoring systems, performing auto-location of a wheel is needed for a number of reasons. Tire pressure monitoring systems generally include a tire pressure monitoring (TPM) sensor in or at each wheel of a vehicle and a central controller which receives tire pressure information from each TPM sensor, to be reported to the driver of the vehicle. Auto-location is the identification of each TPM sensor and determination of its position on the vehicle, automatically and without human intervention. Auto-location may be done initially upon installation and subsequently in the event of tire rotation or replacement. Performing auto-location involves determining the identity or serial number of a TPM sensor in each of the wheels in the car. In premium vehicles, knowing the identity of the TPM sensor in each wheel allows a pressure by position display to be implemented and shown to the driver. In basic vehicles with different placard tire pressures for front and rear axles, it is desirable to know TPM sensor identities and positions in order to check pressure against a correct threshold for an applicable axle.
Auto-location may use antilock brake systems (“ABS”) which are employed in most vehicles. The ABS allows independent wheel speeds to be monitored in near real-time. In one embodiment, the wheel phase and/or speed data includes or is based on the ABS data. The ABS data typically indicates ABS tooth counts. By analyzing ABS tooth counts, correlation between ABS data and other data from TPM sensors can be used to locate wheel positions where the TPM sensors are arranged. ABS sensors provide the ABS data and may be associated with one or more wheels. As one example, ABS sensors are associated with each wheel of a vehicle, or with selected wheels of the vehicle. The wheel phase and/or speed data is not limited to the ABS data. A sensor, a device, a system, or a mechanism that may provide wheel phase and/or speed data directly or in various forms may be used in addition to, or instead of antilock brake systems.
The ABS data may be analyzed statistically. For instance, a historic trace of the ABS data may be observed to determine the location of a wheel based on a statistically significant value of the ABS data, or based on a lowest standard variation of ABS tooth count values. Statistical analysis involving a standard deviation, a variance, dispersion, etc. may fully take even extreme data points into consideration and such data points may significantly influence determination of the location of the wheel. The extreme data points may be caused by nuisance factors such as road noise, vehicle vibrations, error in ABS source data, communication delays, etc. Accordingly, the extreme data points may cause irregular and unexpected changes to the ABS data which may bias the auto-location of the wheel.
The ABS data such as ABS tooth counts increment upwards, regardless of whether a wheel associated with an ABS sensor rotates clockwise or counter clockwise. Any counter clockwise movement over the course of a drive may cause the mean of correlated ABS tooth counts to shift. Accordingly, the counter clockwise movement of the wheel may need to be monitored and upon detection of such movement, it is desirable to take the ABS tooth counts associated with the counter clockwise movement into a consideration in performing the auto-location.